Dipsa

Lucan [1st century CE] ( Pharsalia , book 9,
verse 867-895): "Tyrrhenian Aulus, bearer of
a flag, / Trod on a Dipsas; quick with head
reversed / The serpent struck; no mark
betrayed the tooth: / The aspect of the
wound nor threatened death, / Nor any evil;
but the poison germ / In silence working as
consuming fire / Absorbed the moisture of
his inward frame, / Draining the natural
juices that were spread / Around his vitals;
in his arid jaws / Set flame upon his tongue:
his wearied limbs / No sweat bedewed; dried
up, the fount of tears / Fled from his eyelids.
Tortured by the fire / Nor Cato's sternness,
nor of his sacred charge / The honour could
withhold him; but he dared / To dash his
standard down, and through the plains /
Raging, to seek for water that might slake /
The fatal venom thirsting at his heart. /
Plunge him in Tanais, in Rhone and Po, /
Pour on his burning tongue the flood of
Nile, / Yet were the fire unquenched. So fell
the fang / Of Dipsas in the torrid Libyan
lands; / In other climes less fatal. Next he
seeks / Amid the sands, all barren to the
depths, / For moisture: then returning to the
shoals / Laps them with greed -- in vain --
the briny draught / Scarce quenched the
thirst it made. Nor knowing yet / The poison
in his frame, he steels himself / To rip his
swollen veins and drink the gore. / Cato bids
lift the standard, lest his troops / May find in
thirst a pardon for the deed."
Isidore of Seville [7th century CE]
( Etymologies , Book 12, 4:13): The dipsas is a
kind of asp, called in Latin situla because
anyone bitten by it dies of thirst. (Book 12,
4:32): The dipsas is such a rare snake that
its trampled without being seen. It releases
its poison before it is felt; it causes no grief
to the one who will die because its
appearance anticipates death.